1. Field of the Invention
The present invention relates to a method for detecting an output of a gyroscope, more particularly to a method for detecting an output of, for example, a prism-shaped vibratory gyroscope used a bending vibration.
2. Description of the Prior Art
FIG. 14 is a block diagram showing an example of a detecting circuit used in a conventional method for detecting an output of a gyroscope which is a background of the present invention. The detecting circuit 1 is used for measuring an output of, for example, a triangular prism-shaped vibratory gyroscope 2.
Between two piezoelectric elements 3 and other piezoelectric element 4 of the vibratory gyroscope 2, an oscillation circuit 5 is connected. The oscillation circuit 5 is connected to the piezoelectric elements 3 via resistors 6. Outputs of the piezoelectric elements 3 are applied to a differential circuit 7. An output of the differential circuit 7 is synchronously detected by a synchronized detection circuit 8. The detected signal is amplified by a DC amplifier circuit 9.
By the oscillation circuit 5, the vibratory gyroscope 2 bends and vibrates in the direction perpendicular to the surface whereon the piezoelectric element 4 is formed. In this state, when the vibratory gyroscope 2 is rotated about its axis, the direction of the bending vibration is changed by a Coriolis force. Thereby, a difference of outputs is generated between two piezoelectric elements 3 used as detecting members, an output is obtained from the differential circuit 7. In this case, driving signals for driving the vibratory gyroscope 2 are the same phase and in the same level at two piezoelectric elements 3. Thus, the signals for driving the vibratory gyroscope 2 are offset by the differential circuit 7. Therefore, only a signal corresponding to the magnitude of the rotational angular velocity is obtained from the differential circuit 7. Accordingly, by measuring an output wherein the output of the differential circuit 7 is synchronously detected and DC amplified, the rotational angular velocity applied to the vibratory gyroscope 2 can be measured.
However, by changing the atmospheric temperature and so on, a phase difference is generated between the outputs of the piezoelectric elements for detecting, the phase difference causes to drift. When the phase difference is generated between the outputs of the piezoelectric elements for detecting, since the output of the differential circuit is obtained with the phase difference of about 90 degree against the inputs of the differential circuit, the output of the differential circuit 7 is approximately equivalent in phase to the output signal generated by the Coriolis force depending on the rotational angular velocity. Thus, it is hardly to distinguish the signal by the Coriolis force from the signal by the phase difference between the outputs of the piezoelectric elements, the offset drift is changed by changing the temperature.
Also, by changing the atmospheric temperature and so on, there is a case wherein a level difference is generated between the outputs of the piezoelectric elements for detecting. In such a case, a level difference between the driving signals is obtained from the differential circuit, the level difference causes to drift.